Contrasting Osmotic Stress Responses and Provenance Effects on Seed Germination and Seedling Performance in Two Andean Species

The Andes are currently experiencing prolonged and frequent drought events presenting significant challenges to the natural ecosystems. This study examines how seed provenance and osmotic stress influence germination (radicle and cotyledon emergence) and seedling responses in Oreocallis grandiflora (tree) and Salvia corrugata (shrub), two species with significant potential for maintaining important ecological interactions in the forest. Seeds were collected from individuals in dry and wet provenances of high-elevation mountain forest in Ecuador. Two independent experiments were conducted under controlled and greenhouse conditions. Results revealed marked differences in the drought response of both species. O. grandiflora exhibited greater sensitivity to osmotic stress during seed germination, and seedling mortality occurred within 10 days. However, few seeds from the dry provenance formed their cotyledonary leaves completely, while none from wet provenance germinated. In contrast, S. corrugata had successfully developed radicles and cotyledonary leaves under all osmotic stress treatments across both provenances. Seedlings of this species experienced osmotic stress but recovered within 60 days. Individuals exhibited early- stage adaptations to drought, including defoliation, stomatal conductance and transpiration regulation, and higher leaf relative water content, indicating greater drought tolerance. Provenance effects were strong in O. grandiflora but weak in S. corrugata. Our findings confirm species-specific and provenance-dependent responses to water limitation, emphasizing the importance of selecting appropriate species and seed sources to increase restoration success under climate change scenarios.